Method for the continuous production of cast steel strands

Abstract

A method for the continuous production of cast steel strands which are 200 mm×200 mm or less in cross-section by a continuous casting process in which molten steel containing 0.20% or less of carbon is fed into a casting mold with a lubricant through a submerged nozzle or in an open stream and continuously drawn out downwardly of the casting mold. The method includes the steps of (a) electromagnetically stirring the molten steel at a position within said casting mold by the application of a magnetic field induced by introducing into an electromagnetic coil an alternating current of a frequency (f) in the range of 1.5 to 15 hertz and maintaining the magnetic flux density (Gaub) in the range of 602e -0 .10f to 2441e -0 .11f at the center of the electromagnetic coil, and (b) electromagnetically stirring the molten steel at a position in the final solidifying zone, of said continuously cast strand, in which the shorter diameter of the molten steel pool is smaller than 1/2 the length of the shorter side of the cast strand, by the application of a magnetic field induced by introducing an alternating current into an electromagnetic coil and maintaining the magnetic flux density (Gaub) in the range of 0.2·D 2 +280 to 0.343·D 2 +451 at the center of the electromagnetic coil, wherein D is the solidified shell thickness in millimeters of said continuously cast strand, the value of D ranging from 20 to 90. The method thereby permits the production of low carbon killed steel billets which are improved as to negative segregations, center cavities, inclusions, surface quality, cold forgeability, and machinability, by a continuous casting process at low cost.

What is claimed is: 
     
       1. A method for the continuous production of cast steel strands which are 200 mm×200 mm or less in cross-section by a continuous casting process in which molten steel containing 0.20% or less of carbon is fed into a casting mold with a lubricant and continuously drawn out downwardly of the casting mold, said method comprising the steps of: (a) electromagnetically stirring the molten steel at a position within said casting mold by the application of a magnetic field induced by introducing into an electromagnetic coil an alternating current of a frequency (f) in the range of 1.5 to 15 Hz and maintaining the magnetic flux density in the range of 602 e -0 .10f to 2441 e -0 .11f gauss at the center of the electromagnetic coil, and   (b) electromagnetically stirring the molten steel at a position in the final solidfying zone of said continuously cast strands in which the shorter diameter of the molten steel pool is smaller than 1/2 the length of the shorter side of the cast strand, by the application of a magnetic field induced by introducing an alternating current having a freqency in the range of 50 to 60 Hz into an electromagnetic coil and maintaining the magnetic flux density in the range of 0.2·D 2  +280 gauss to 0.343·D 2  +451 gauss at the center of the electromagnetic coil, wherein D is the solidified shell thickness in millimeters of said continuously cast strands, the value of D ranging from 20 to 90.   
     
     
       2. A method according to claim 1, which further comprises the step of electromagnetically stirring the molten steel at a position in the intermediate solidifying zone of said continuously cast strand by the application of a magnetic field induced by introducing an alternating current into an electromagnetic coil and maintaining the magnetic flux density in the range of 750000/(D-110) 2  gauss to 750000/(D-81) 2  gauss at the center of the electromagnetic coil, wherein D is the solidified shell thickness in millimeters of said continuously cast strand, the value of said D ranging from 10 to 50, and said intermediate solidifying zone being a zone between said casting mold and said final solidifying zone. 
     
     
       3. A method according to claim 1 or 2, wherein said lubricant is oil or powder. 
     
     
       4. A method according to claim 3, wherein said lubricant is powder and said magnetic flux density at the center of the electromagnetic coil in said casting mold is in the range of 602e -0 .10f gauss to 1339e -0 .12f gauss. 
     
     
       5. A method according to claim 1, wherein said stirring in the final solidifying zone is induced by an intermittent electric current. 
     
     
       6. A method according to claim 1, wherein said stirring in the final solidifying zone is induced by an electric current the polarity of which is periodically inverted. 
     
     
       7. A method of producing continuously cast strands which are less than 200 mm×200 mm in cross-section by a continuous casting process in which molten steel containing 0.20% or less carbon and a lubricant is fed into a casting mold and continuously drawn out downwardly of the casting mold, said method comprising the steps of: (a) electromagnetically stirring the molten steel at a position within said casting mold by application of a magnetic field induced by an alternating current of a frequency f of between 1.5 Hz and 15 Hz and having a magnetic flux density G at the center of the molten steel in the range of 602 e -0 .10f gauss to 2,441 e -0 .11f gauss, and also   (b) electromagnetically stirring the molten steel at a position in the final solidifing zone of each of said continuously cast strands by application of a magnetic field induced by an alternating current having a frequency in the range of 50 to 60 Hz and having a magnetic flux density G at the center of the molten steel in the range of 0.2 D 2  +280 gauss to 0.343 D 2  +451 gauss, where D is the solidified shell thickness of each of said continuously cast strands in millimeters, said final solidifying zone being defined as a zone where the molten steel in each of said continuously cast strands is present as a molten steel pool having a generally circular or ovular cross-sectional shape, in which the shorter diameter of the molten steel pool is less than 1/2 the length of the shorter side of the cast strand, and the value of D is between 20 and 90.   
     
     
       8. A method as recited in claim 7 and further comprising the step of electromagnetically stirring the molten steel at a position in an intermediate solidifying zone of each of said continuously cast strands by application of a magnetic field induced by an alternating current and having a magnetic flux density G at the center of the molten steel in the range of 750,000/(D-110) 2  gauss to 750,000/(D-81) 2  gauss, where D is the solidified shell thickness of each of said continuously cast strands in millimeters, said intermediate solidifying zone being defined as a zone between said casting mold and said final solidifying zone in which the value of D is between 10 and 50. 
     
     
       9. A method as recited in claim 7 or 8 wherein said lubricant is oil or powder. 
     
     
       10. A method as recited in claim 7 or 8 wherein: (a) said lubricant is powder and   (b) the magnetic flux density G at the center of the molten steel in said casting mold is in the range of 602e -0 .10f gauss to 1,339e -0 .12f gauss.   
     
     
       11. A method as recited in claim 7 wherein the electromagnetic stirring in said final solidifying zone is induced by an intermittent electric current. 
     
     
       12. A method as recited in claim 7 wherein the electromagnetic stirring in said final solidifying zone is induced by an electric current the polarity of which is periodically inverted.